This invention relates to catalysts comprising microporous, microcrystalline aluminum phosphates and zeolites and to conversions, e.g., hydrocarbon conversions, with these catalysts.
Aluminum phosphates are taught in U.S. Pat. Nos. 4,310,440 and 4,385,994, for example. Aluminum phosphate materials have electroneutral lattices and, therefore, are not particularly useful as ion-exchangers or as catalyst components. Microporous aluminum phosphates may have an organic amine or quaternary ammonium salt entrapped within the aluminum phosphate and playing a role as crystallization template. In addition to this organic template, water may fill the microporous voids of the aluminum phosphate, especially in its as synthesized form. Because of the aluminum/phosphorus atomic ratio of these materials being about unity, they display virtually no ion-exchange properties, the framework positive charge on phosphorus being balanced by corresponding negative charge on aluminum: EQU AlPO.sub.4 =(AlO.sub.2.sup.-)(PO.sub.2.sup.+)
U.S. Pat. No. 4,310,440 indicates that the aluminum phosphates described therein may be used as catalysts or catalyst bases. With regard to the latter use it is noted that these aluminum phosphates may be impregnated with catalytically active metals. Note column 47, lines 40-49 of this U.S. Pat. No. 4,310,440. However, there is no particular statement in this patent that the aluminum phosphates may be used as catalysts or catalyst bases in combination with zeolites.
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure as determined by X-ray diffraction, within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties.
Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline aluminosilicates. These aluminosilicates can be described as a rigid three-dimensional framework of SiO.sub.4 and AlO.sub.4 in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total aluminum and silicon atoms to oxygen atoms is 1:2. The electrovalence of the tetrahedra containing aluminum is balanced by the inclusion in the crystal of a cation, for example an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of aluminum to the number of various cations, such as Ca/2, Sr/2, Na, K or Li, is equal to unity. One type of cation may be exchanged either entirely or partially with another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given aluminosilicate by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
Prior art techniques have resulted in the formation of a great variety of synthetic zeolites. The zeolites have come to be designated by letter or other convenient symbols, as illustrated by zeolite A (U.S. Pat. No. 2,882,243), zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S. Pat. No. 3,130,007), zeolite ZK-5 (U.S. Pat. No. 3,247,195), zeolite ZK-4 (U.S. Pat. No. 3,314,752), zeolite ZSM-5 (U.S. Pat. No. 3,702,886), zeolite ZSM-11 (U.S. Pat. No. 3,709,979), zeolite ZSM-12 (U.S. Pat. No. 3,832,449), zeolite ZSM-20 (U.S. Pat. No. 3,972,983), ZSM-35 (U.S. Pat. No. 4,016,245), ZSM-38 (U.S. Pat. No. 4,046,859), and zeolite ZSM-23 (U.S. Pat. No. 4,076,842), merely to name a few.
The SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of a given aluminosilicate zeolite is often variable. For example, zeolite X can be synthesized with SiO.sub.2 /Al.sub.2 O.sub.3 ratios of from 2 to 3; zeolite Y, from 3 to about 6. In some aluminosilicate zeolites, the upper limit of the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is unbounded. Aluminosilicate ZSM-5 is one such example wherein the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is at least 5 and up to infinity. U.S. Pat. No. 3,941,871 (Re. 29,948) discloses a porous crystalline silicate made from a reaction mixture containing no deliberately added alumina in the recipe and exhibiting the X-ray diffraction pattern characteristic of ZSM-5 type zeolites. U.S. Pat. Nos. 4,061,724, 4,073,865 and 4,104,294 describe crystalline silicates or organosilicates of varying alumina and metal content.
A number of synthetic zeolites have been prepared which may be said to be isostructural with naturally occurring zeolites. Zeolites ZSM-35 and ZSM-38 are, for instance, ferrierite-type zeolites. Zeolite ZK-20 (U.S. Pat. No. 3,459,676) is described as being isostructural with the naturally occurring zeolite levynite.
Although zeolites may contain silica and alumina, it is recognized that the silica and alumina portions may be replaced in whole or in part with other oxides. More particularly, GeO.sub.2 is an art recognized substitute for SiO.sub.2 and B.sub.2 O.sub.3, Cr.sub.2 O.sub.3, Fe.sub.2 O.sub.3, and Ga.sub.2 O.sub.3 are art recognized replacements for Al.sub.2 O.sub.3. Accordingly, the term zeolite as used herein shall connote not only materials containing silicon and, optionally, aluminum atoms in the crystalline lattice structure thereof, but also materials which contain suitable replacement atoms for such silicon and/or aluminum. On the other hand, the term aluminosilicate zeolite as used herein shall define zeolite materials consisting essentially of silicon and, optionally, aluminum atoms in the crystalline lattice structure thereof, as opposed to materials which contain substantial amounts of suitable replacement atoms for such silicon and/or aluminum.
As mentioned previously, the catalysts of the present invention may be used in hydrocarbon conversions. Examples of such conversions are dewaxing processes.
Catalytic dewaxing of hydrocarbon oils to reduce the temperature at which separation of waxy hydrocarbons occurs is a known process. A process of that nature is described in The Oil and Gas Journal dated Jan. 6, 1975, at pages 69-73. See also U.S. Pat. No. 3,668,113 and U.S. Pat. No. 3,894,938 which describe dewaxing followed by hydrofinishing.
U.S. Pat. No. Re. 28,398 describes a process for catalytic dewaxing with a catalyst comprising a zeolite of the ZSM-5 type. A hydrogenation/dehydrogenation component may be present.
A process for hydrodewaxing a gas oil with a ZSM-5 type catalyst is described in U.S. Pat. No. 3,956,102.
A mordenite catalyst containing a Group VI or a Group VIII metal is used to dewax a low V.I. distillate from a waxy crude, as described in U.S. Pat. No. 4,110,056.
Other patents which describe various catalytic dewaxing processes include U.S. Pat. Nos. 3,755,138; 4,053,532; 4,247,388; 4,474,618; and 4,486,296.
Catalytic dewaxing may be employed to dewax a variety of distillate feedstocks such as gas oils, coker bottoms, reduced crudes, recycle oils and FCC bottoms. Catalytic dewaxing may also be employed to dewax various lube stocks.
Refining suitable petroleum crude oils to obtain a variety of lubricating oils which function effectively in diverse environments has become a highly developed and complex art. Although the broad principles involved in refining are qualitatively understood, the art is encumbered by quantitative uncertainties which require considerable resort to empiricism in practical refining. Underlying these quantitative uncertainties is the complexity of the molecular constitution of lubricating oils. Because lubricating oils for the most part are based on petroleum fractions boiling above about 450.degree. F., the molecular weight of the hydrocarbon constituents is high and these constituents display almost all conceivable structure types. This complexity and its consequences are referred to in well-known treatises, such as, for example, in "Petroleum Refinery Engineering", by W. L. Nelson, McGraw Hill Book Company, Inc., New York, N.Y., 1958 (Fourth Edition).
In general, the basic premise in lubricant refining is that a suitable crude oil, as shown by experience or by assay, contains a quantity of lubricant stock having a predetermined set of properties such as, for example, appropriate viscosity, oxidation stability, and maintenance of fluidity at low temperatures. The process of refining to isolate that lubricant stock consists of a set of subtractive unit operations which removes the unwanted components. The most important of these unit operations include distillation, solvent refining, and dewaxing, which basically are physical separation processes in the sense that if all the separated fractions were recombined one would reconstitute the crude oil.
A refined lubricant stock may be used as such as a lubricant, or it may be blended with another refined lubricant stock having different properties. Or, the refined lubricant stock prior to use as a lubricant, may be compounded with one or more additives which function, for example, as antioxidants, extreme pressure additives, and V.I. improvers.
For the preparation of a high grade distillate lubricating oil stock, the current practice is to vacuum distill an atmospheric tower residuum from an appropriate crude oil as the first step. This step provides one or more raw stocks within the boiling range of about 450.degree. F. to 1050.degree. F. After preparation of a raw stock of suitable boiling range, it is extracted with a solvent, e.g., furfural, phenol, sulfolane, or chlorex, which is selective for aromatic hydrocarbons, and which removes undesirable components. The raffinate from solvent refining is then dewaxed.
If the resulting lube stock is not dewaxed catalytically, it is generally dewaxed by admixing with a solvent such as a blend of methyl ethyl ketone and toluene. The mixture is chilled to induce crystallization of the paraffin waxes which are then separated from the raffinate. Sufficient quantities of wax are removed to provide the desired pour point for the raffinate.
Other processes such as hydrofinishing or clay percolation may be used if needed to reduce the nitrogen and sulfur content or improve the color of the lubricating oil stock.
The entire disclosures of the above-mentioned U.S. patents are expressly incorporated herein by reference.